1. Field of the Invention
The present invention relates to a direct-view-type display apparatus using organic thin-film EL elements as display elements, for example, and particularly to a direct-view-type display apparatus suitable for realizing a large display screen.
2. Description of the Related Art
EL (electroluminescent) elements are known as a kind of light-emitting display elements. EL elements make use of an electro-luminescence as a principle which is a phenomenon in which a light is produced from a phosphor when applied with a voltage.
From a standpoint of a chemical composition of a light-emitting material, EL elements are classified into an inorganic EL element in which rare earth element serving as a center of light emission is added to a host material made of an inorganic compound and an organic EL element using a fluorescent organic compound. From a standpoint of a physical shape of a light-emitting material, EL elements are classified as a dispersion-type EL element using a powder-like light-emitting material and a thin-film EL element using a dense thin-film-like light-emitting material.
Since the organic thin-film EL element is able to display colors that matches with fluorescent colors of organic compounds so that colors can be selected with ease as compared with the inorganic EL element, it can be driven by a low drive voltage as compared with the inorganic EL element and it can easily be manufactured by microminiaturization as compared with the inorganic EL element, in recent years, it is receiving a remarkable attention as a display element for use in a direct-view-type display apparatus.
The direct-view-type display apparatus using this organic thin-film EL element (hereinafter simply referred to as an xe2x80x9corganic EL displayxe2x80x9d) has an advantage that it can be well confirmed visually as compared with display apparatus using a non-light-emitting display element such as a liquid crystal and has also an advantage that it can do with a low driving voltage as compared with display apparatus using a display element of another light-emitting type (e.g., plasma display and field-emission display) so that it consumes less power and it can be expected that ICs for driving this type of display element can be manufacured inexpensively.
In recent years, needs for enlarging display screens of various kinds of indoor and outdoor displays are increasing. In the organic EL display, when the size of the organic thin-film EL element itself is increased, lengths of signal electrodes and scanning electrodes comprising the organic thin-film EL element are increased and resistance of these electrodes increase so that a drive voltage should be increased. For this reason, heretofore, it has been difficult to realize an organic EL display of a large picture screen. This is also true in other flat panel displays such as a PDP (plasma display panel), an FED (field-emission display) and an LCD (liquid-crystal panel).
FIG. 13 shows an example of an arrangement of this display unit. A display unit 51 is manufactured such that a protecting film (not shown) made of an inorganic compound such as GeO is formed on the surface of an organic thin-film EL element 53 formed on a glass substrate 52 or a light-curing resin layer (not shown) is formed directly or through an SiO2 film on which a glass plate 54 having the same area as that of the glass substrate 52 is tightly contacted and the glass plate 54 and the glass substrate 52 are bonded together at end portions of their plate surfaces by an adhesive agent 55 having an end-sealing property. FIG. 14 shows an example in which a plurality of display units 51 shown in FIG. 13 are disposed in a matrix fashion.
The reason that the organic thin-film EL element is sealed by the glass plate 54 and the adhesive agent 55 as shown in FIG. 13 is as follows. That is, an organic compound used in an organic layer of the organic thin-film EL element is considerably weak to water and oxygen, and metals comprising anodes and cathodes of the organic thin-film EL element also are oxidized in the air and their characteristics are deteriorated suddenly.
However, when the large picture screen of the organic EL display is realized by disposing a plurality of display units in a matrix fashion as described above, there are various disadvantages which will follow.
(a) Since each of the display units should be positioned with high accuracy in order to maintain a periodicity with which pixels are arrayed on the whole of the picture screen, a fabrication work becomes complicated and a manufacturing cost increases.
(b) After fabrication, there is a risk that a positional relationship between the display units is being shifted slightly with a change in the environment (temperature change, etc.) and the the passage of time, so that the periodicity of the pixels array will be lost.
(c) Since a boundary between the transparent substrates (glass substrate 52 in FIG. 13) of each display unit is visually spotted as a joint on the picture screen, a picture quality is deteriorated.
(d) Since needs for increasing resolution as well as the size of the picture screen also are increasing, pitches between pixels should be minimized in order to meet the above needs. However, according to the sealing method in which the glass substrates are bonded at their end portions as shown in FIG. 13, since the organic thin-film EL element cannot be formed on the end portions (portions of widths L in the sheet of drawing) of the glass substrate surfaces (i.e., pixel cannot be provided), if the pixel pitch is increased at least twice this width L, there cannot be maintained the periodicity with which the pixels are arrayed on the whole of the picture screen. Accordingly, it is difficult to increase resolution.
In view of the aforesaid aspects, the present invention is intended to realize the organic EL display with the large picture screen and to do away with the above disadvantage (a) and to simplify the fabrication work and to reduce the manufacturing cost, to do away with the above disadvantage (b) and to maintain the periodicity with which the pixels are arrayed on the whole of the picture screen after fabrication, to do away with the above disadvantage (c) and to prevent a picture quality from being deteriorated due to the boundary between the transparent substrates, and to do away with the above disadvantage (d) and to realize the picture screen of the high resolution.
While the organic EL display has been described so far by way of an example, it is unavoidable that direct-view-type display apparatus other than the organic EL display encounters at least the above disadvantages (a) to (d) when a display element is formed as a unit and a plurality of display units are disposed in a matrix fashion.
Accordingly, the present invention is to provide a direct-view-type display apparatus other than the organic EL display in which a large picture screen can be realized, the fabrication work can be simplified, the manufacturing cost can be reduced, the periodicity with which the pixels are arrayed on the whole of the picture screen can be maintained and the deterioration of the picture quality can be prevented.
To solve these problems, a direct-view-type display apparatus according to the present invention is characterized in that a plurality of display elements are formed on a single transparent substrate and driver circuits for supplying signals to signal electrodes and scanning electrodes of these display elements are provided in response to respective display elements.
In this direct-view-type display apparatus, a plurality of display elements are not formed as units like the prior art but are formed on a single, common transparent substrate. Then, when signals are supplied to the respective display elements from the corresponding driver circuits, an image is displayed on one picture screen of this transparent substrate.
Because a plurality of display elements are formed on the single, common transparent substrate as described above, the periodicity with which the pixels are arrayed on the whole of the picture screen can be maintained without positioning the display units with high accuracy unlike the prior art, the large picture screen can be realized, the fabrication work can be simplified and the manufacturing cost can be reduced.
Because the positional relationship between the display elements can be prevented from being shifted after fabrication unlike the case in which a plurality of display units are disposed in a matrix fashion, the periodicity with which the pixels are disposed on the whole of the picture screen can be maintained after fabrication.
Since there does not exist the boundary between the transparent substrates of the respective display units unlike the prior art, the picture quality can be prevented from being deteriorated due to the above boundary.
In this direct-view-type display apparatus, by way of an example, it is suitable that the circuit substrate on which the driver circuits are mounted in response to the respective display elements are disposed on the back side (opposite to the display surface).
Since the positioning of the circuit substrate relative to the display element is required to such an extent that the driver circuits may electrically be connected to the electrodes of the display elements, the highly-accurate positioning of the display units is not required unlike the prior art. Therefore, the fabrication work can be prevented from becoming complicated and the manufacturing cost can be prevented from being increased.
When the display element is the organic EL element (i.e., organic EL display), by way of an example, the height of the signal electrode and the height of the scanning electrode of the organic EL element on the transparent substrate are made substantially equal to each other. The circuit substrate is made of a material having end-sealing property and has through-holes bored at its positions opposing to the signal electrode and the scanning electrode. The through-holes are buried by a material having end-sealing property and conductivity. While the through-holes are being opposed to the signal electrode and the scanning electrode, the circuit substrate is closely bonded to the organic EL element. Signals are supplied from the driver circuit through the material having the end-sealing property and the conductivity. The organic EL element is covered at its portion which is not bonded to the circuit substrate with an end-sealing material.
Since the organic EL element is sealed by the circuit substrate, the material having an end-sealing property and a conductivity and the end-sealing material while the space between the adjacent organic EL element on the transparent substrate is being kept narrow, the pixel pitch can be reduced, and therefore the organic EL display with high resolution can be realized.
By way of an example, it is suitable that the transparent substrate should be formed of a film-like substrate. According to this arrangement, not only a flat picture screen can be formed but also a curved picture screen can be formed by curving this transparent substrate.
By way of another example, it is suitable that the side surface of the circuit substrate should be covered with a member having an elasticity. According to this arrangement, even if the circuit boards are butted against each other when the circuit boards are disposed or the curved picture screen is formed by curving the transparent substrate, the circuit boards can be prevented from being chipped or scratched.